1. Technical Field
The present invention relates to shrinkage compensating concrete slab structures. In particular, it relates to a reinforced shrinkage compensating concrete slab structure having first and second reinforcing bar arrays which define a centroid and peripheral portions so that active expansive and shrinkage forces are restrained.
2. Background Art
The construction of shrinkage compensating concrete slab structures is generally known. Such constructions are sometimes referred to as “self-stressing concrete” and to “chemically prestressed concrete.” Unlike traditional Portland cement based concrete, the shrinkage compensating concrete has a constituent that actively causes the concrete to volumetrically enlarge. According to the American Concrete Institute (“ACI”), shrinkage compensating concrete means “a concrete that, when strained by reinforcement or other means, expands . . . [and] ideally, a residual expansion will remain in the concrete, thereby eliminating shrinkage cracking.” The restraint of cracking in shrinkage compensating concrete is thus elemental to its function.
Unlike prestressed concrete and post-tensioned concrete, where the concrete is passive and the restraint actively acting upon the concrete from either pre- or post-tensioning the reinforcement, shrinkage compensating concrete generates its own expansive forces which, in turn, tension the reinforcement. ACI further references the term restraint as meaning “a resilient type of restraint, such as that provided by internal reinforcement, shall be provided to develop shrinkage compensation. Other types of restraint, such as adjacent structural elements, sub-grade friction, and integral abutments are largely indeterminate and provide either too much or too little restraint.”
Industry guidelines further provide definitive provisions which relate to the amount of reinforcement required to restrain shrinkage in shrinkage compensating concrete slabs. These guidelines provide guidance as to an accepted volume and presence of embedded steel reinforcing bars in relation to the cross-sectional area of concrete to be poured. However, the overall design configuration of the actual layout of the reinforcing bars is largely left to the one who specifies the job excepting, however, certain recommendations as to the configuration of the construction of the slab with wire mesh and/or deformed reinforcing bar in a two-way reinforcement pattern.
Related technologies are also disclosed which relate to the science of making and using various pre-tension and post-tension methods and constructions with plastic coated wire, cable, and certain reinforcing bar designs for dealing with the compressive forces acting on the slab during its construction. However, such methods and materials, including the use of tension bands are costly, time consuming, and require the use of passive concrete and active compression dynamics. For example, U.S. Pat. No. 2,035,007, to Workman, discloses a concrete construction where the structure includes subdivided circular areas producing circumferential stress bands areas alternating between compressive stresses in the alternative bands.
Moreover, U.S. Pat. No. 3,513,609, to Lang, discloses the use of reinforcing “tendons”, of a plastic coated wire having a low friction interface between the wire and the coating. The tendons are integrated in a common plane for use in post-tensioning a concrete construction. U.S. Pat. No. 3,710,526, to Parks, discloses a floor construction wherein pre or post stressed, radially extending tendons are placed within an annular compression beam. In this construction, a reinforced annular girder is precast. After the cement has set high tensile, radially extending tendons are prestressed. Concrete is then placed in areas defined as a web and annulus slab. After the concrete has set the tension is relieved, and the beam is ready for use as floor construction.
Certain disclosures illustrate the use of a reinforcing bar configuration to elastically restrain expansive and shrinkage forces in a concrete slab construction. For Example, U.S. Pat. No. 6,470,640, to Ytterberg, discloses a reinforced concrete building structure including a shrinkage compensating concrete slab. The slab includes a plurality of deformed reinforcing bars embedded therein. The bars are restricted to a peripheral portion of the slab, which surrounds the centroid of the slab, devoid of reinforcement, and are aligned with the expansive and shrinkage forces to elastically restrain the forces and to thereby act as an internally developed tension ring.
While the foregoing methods and materials are useful in providing designs for the construction of shrinkage compensating concrete slab structures, there is still a need for alternate constructions which are useful to elastically restrain the expansive and shrinkage forces upon a shrinkage compensating slab structure, but which are characterized, by certain criteria including overall simplicity and economy in construction. The present invention satisfies these needs.